To produce high purity mono-terpenes (alpha-Terpinene and d-Limonene) for use in electronic materials of construction for integrated circuits is problematic due to the very high purity requirements of the electronics fabrication industry and the necessary electrical properties of materials to have operable devices. Alpha-terpinene, as an example, is extracted from wood chips and is commercially available at its highest purity at around 90% (all % herein are vol. %). At the highest available purity, it still contains four main impurities, with Eucalyptol (1,8-Cineole) ranging from 1-5%. Traditional methods for removing the impurities, such as distillation, are not effective due to the similar boiling points of the desired product and all of the impurities (175-176° C.).
Scheffer, J. J. C; “Improved Gas Chromatographic Analysis of Naturally Occuring Oxygen containing Monoterpenes Following Prefractionation by Liquid—Solid Chromotography”; Chromatographia (November 1977), 10 (11), 669-677, uses carrier solvents, such as ethanol and pentane in a gradient, to separate differing oxygenated monoterpenes along a deactivated silica gel column, which silica gel contains water to maintain its deactivated condition and not isomerizes the oxygenated monoterpenes. The products must be separated from the eluting solvent and the silica gel must be deactivated to avoid isomerizing the products.
GB 194286 discloses that essential oils and terpene hydrocarbons are purified by treatment with a suitable material which reacts with the impurities present, then adding an “agglomerating agent,” and finally removing the solid substances. As agents for acting upon the impurities, “active” halogen compounds, such as alkali or alkaline earth hypochlorites are mentioned, fuller's earth, silica gel, boneblack or other decolorizing charcoal are given as examples of the “agglomerating agents”; while the starting materials specified are oils of copaiba, fir cones, ginger, juniper, pepper, pine, cedar and peppermint, as well as pinene, dipentene, limonene and isoprene. This process uses water in the separation process and reacts the sulfur containing compounds which cause odor before agglomerating the reacted compounds on materials such as silica gel before mechanical separation of the desired turpentine product.
The present invention overcomes the deficiencies of the prior art in purifying mono-terpenes of oxygen-containing impurity compounds without the requirement for the use of additional chemical reagents or elution solvents so as to recover a neat product and recognizing the particular detriment of such oxygen-containing impurity compounds in electronic materials use, as will be set forth in greater detail below.